Terminator-style liquid metal connects severed nerves

Hasta la vista, nerve damage. Experiments with bullfrog nerves show that a Terminator-style liquid metal alloy could one day be placed in the body to help severed nerves reconnect. The alloy would stay in place until the nerve has healed, before being slurped back out with a syringe.

The peripheral nervous system consists of nerves that carry electrical signals from the brain to the rest of the body. Because they aren't protected by the spine or the skull, peripheral nerves are more vulnerable to injuries than those in the central nervous system.

Severed nerves can reconnect if treated quickly enough, but at a rate of just 1 millimetre per day. Also, existing methods for grafting nerve ends back together have serious shortcomings. For instance, most existing scaffolds for grafts must ultimately be removed, requiring risky follow-up surgery. Even more worrisome, if the nerves don't pass signals to muscles during the healing process, the muscles can atrophy to the point where they never fully recover.

"Taking the functional recovery into consideration during the regeneration is of great significance for patients," says Jing Liu at Tsinghua University in Beijing, China.

Making the cut

Liu and his colleagues wondered if liquid metal could act as a backup system for damaged nerves, helping signals pass through a graft while the nerve healed. They used an alloy of gallium, indium and tin, which is a very good electrical conductor. The alloy is liquid at room temperature, allowing it to be removed with a syringe when it's no longer needed.

To show that the alloy works, the team tested it on the sciatic nerve of 10 bullfrogs. After removing the nerve, they measured the strength of electrical impulses that pass from one end of the nerve into the frog's calf muscle. Then they cut the nerve and reconnected the ends with tubes containing either the liquid metal or Ringer's solution, a mix of salts designed to mimic body fluids and preserve the flow of electrical impulses.

The nerves reconnected with liquid metal conducted electrical signals about as well as a healthy nerve, and several orders of magnitude better than nerves reconnected with Ringer's solution, says Liu. The team also injected some of the metal alloy into a severed frog's leg. They were able to easily find the fluid in X-rays and remove it with a syringe.

Safety first

In future, Liu envisions that the alloy could become part of a graft also filled with a solution that promotes nerve growth. The team has proposed a few designs for such a device.

"It looks like it's innovative and believable," says Mei Zhang at Zyno Medical, who studied nerve regeneration before leaving academia. She still has concerns about the safety of using liquid metal in people, however. "If it gets into your bloodstream, in the worst case you could be poisoned."

Liu agrees that this study is just a starting point, and he intends to do more animal tests soon. "Of course, before use in clinics, tremendous evaluations about the safety of the material are needed," he says. "This is a brand new trial in its initial stage."

Correction, 17 June 2014:When this article was first published, we got our wires crossed. The alloy used contains gallium, indium and tin.

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The metal alloy GaInSn is easily picked up by X-ray (left) and removed (right) (Image: Courtesy of Professor Jing Liu at Tsinghua University)